Honestly the Quad CAN be tuned to work very well. There are several folks posting here that say they are getting 11-12 mpg with their MH. My pull truck for our Airstream is a 88 454 Subruban with a TH400. I barely get 10 mpg. I have put it on a exhaust analyizer thing I had misxture problems and I don't. The Quad just seems to do a little better once it gets up to cruise. I think it leans out a hair more then the FI does.
As for converting. I'm about to under go this conversion on one of my trucks. It's possible to do but there are some vairables you need to be aware of. The cam in your engine is a different grind then what a 454 that was set up for FI is. Knock sensors are not all the same. They are tuned to the block.
Vehicles I would recomend as a doaner would be 87-91 GM Suburbans and Crew cabs with the 454. The 454 throttle body with the preheat riser is a bolt on in place of a carb. The 350cid version is not. The FI in these trucks was almost like a aftermarket FI set up. THe main harness is completely seperat from the rest of the vehicles harness. 87-85 454 van would also be a simular set up.
If you want to save yourself a lot of hassle then contact
http://www.customefis.com/index.html This guy has a small buisness where if pulls used FI, Flow tests the injectors, makes a NEW harness and sells it as a kit. He can custom tailor a chip to work with that cam. He also has a link to WinADSL shareware. This is a program you can install on a lap top and plug into the test port and get real time ECM readings. You can also data log it and he can fine tune the chip to the engine from that information.
Tell him the guy From ColoradK5 sent you.
I'm about to get him to put me together a system for my 4x4.